If global temperatures rise by 1 degree Celsius (C) or more above current levels, billions of people each year will be exposed to heat and humidity so extreme that they will be unable to cool themselves naturally, according to interdisciplinary research from Penn State's College of Health and Human Development, Purdue University's College of Science and the Purdue Institute for a Sustainable Future. The results of a new paper published today (October 9) in Proceedings of the National Academy of Sciences have indicated that global warming beyond 1.5°C above pre-industrial levels will be increasingly devastating to human health across the planet. People can only tolerate certain combinations of heat and humidity before their bodies start to experience heat-related health problems like heatstroke or heart attacks. As climate change raises temperatures around the world, billions of people could be pushed beyond these limits. (Pennsylvania State University)